Help installing Plugins

Well as the title suggest I need help with installing plugins.
I am trying to install a plugin that lets you use LaTex but am unable to do so. All the FAQs I have read mention a "wp-resources/dirctory" or something like that, and I have no idea where to find this. Also when I went to the administrative part of my site the section on plugins was not very useful.
Could someone please provide me with a step by step guide on how to install plugins?